The present disclosure relates generally to downhole neutron generators, methods to generate neutrons in a downhole environment, and methods to log formation data.
Oil and gas companies often utilize different logging techniques to obtain a record of petrophysical properties of a formation, such as, but not limited to, formation resistivity, formation anisotropy, dip angle of formation bed, radioactivity of the formation, formation density, formation porosity, acoustic properties of the formation, and formation pressure properties as well as other properties of the formation (collectively referred to as “formation properties”). For example, in wireline logging, a logging tool is attached to a wireline and is lowered into a borehole. The logging tool contains various sensor components used to obtain the formation properties. Data corresponding to the measurements may be recorded in real time mode or in memory mode.
Some conventional logging tools utilize always-on, radioactive chemical sources that generate energetic particles, such as neutrons and gamma-rays that interact with the surrounding formation, and utilize sensors to detect resulting signals indicative of the formation properties of the surrounding formation. However, many of the chemical sources are hazardous to the downhole environment. Other logging tools utilize pulsed neutron generators to generate neutrons that interact with the surrounding formation. The logging tools also utilize sensors to detect resulting signals indicative of the properties of the surrounding formation.
Certain types of neutron generators utilize penning discharge ion sources, which include permanent magnets or solenoids to initiate ionization of deuterium and tritium gas in an ionization chamber or an ion source. However, magnetic properties deteriorate at operational temperatures of the neutron generators. Further, solenoids require additional electrical connections and circuitry, which complicate the design and increases the cost of the neutron generators.
Other types of neutron generators utilize electron impact ionization as well as direct field ionization techniques to initiate ionization of deuterium and trillium gases. However common designs of neutron generators that utilize the foregoing techniques also utilizes an Ultra High voltage (“UHV”) section to accelerate deuterium and trillium ions. The UHV unit is often housed in a cavity having an outer diameter of approximately 1½ inches and a length of approximately 5 feet. In a downhole environment, the length of the UHV unit significantly increases the size, complexity, and cost of the neutron generators. Further, it may not be feasible to deploy the UHV in an annulus of a production casing or a wellbore due to the dimensions of the UHV.
The illustrated figures are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented.